I would like to ask how do we reference a chart especially if the contents are mostly medical terms and very difficult to rephrase?

Answers

If tables or charts are reproduced exactly as they appear in a source then the name of the author, year and page number must be given. If the chart was found on page 10, your in text citation should look like:

If the chart has been used from a journal article, and nothing else from that article has been used, and the chart was created by the author of the journal article, then in your reference list, insert the word chart before the journal title, and replace the page range of the article with the page number of the chart.